U.S. Pat. No. 4,420,447 issued Dec. 13, 1983 discloses a mold apparatus having a cavity block and a cavity core which are operated to receive skin, insert and foam components which are combined to define a finished composite article. U.S. Pat. Nos. 1,973,550; 2,336,578; 2,757,426; 3,325,861; 3,380,121; and 3,643,911 disclose various liners for mold tooling. They do not disclose a method for balancing mold tooling by the process of the present invention including use of reuseable, thermally stable alloy material and use of a theoretical and an actual part replica to form balanced liner components.
The current method for making the cavity block and cavity core components of such apparatus includes use of a sand mold formed by a wood or epoxy mandrel shaped to conform to the mold tool configuration. The sand mold cavity is filled with aluminum to form the tool. Aluminum has an inherent shrinkage in the range of 0.013 inches and consequently the mandrels are constructed oversized (with a 0.013 inch expansion factor) to compensate for shrinkage.
Such compensation has its faults since in real practice cast aluminum does not have the same shrinkage over all sections and over all dimensions of the casting due in part to different rates of cooling caused by the part configuration and casting methods. As a result, tools made by this method do not always match with a theoretically perfect skin or insert carried thereon during the manufacture of a composite article comprising a skin, an insert and foam material.
In real practice the skin and insert also will vary in shape and form making the fit problem even more difficult.
To alleviate the problem such cast aluminum tools are "balanced" by a process which accounts for the afore-described discrepancies. Such balancing may involve shimming, epoxy filling, sanding and grinding of the cast aluminum pour tools to change the fit between them and the insert and skin supported thereon.
The balancing process must be repeated for each set of tools and can involve a considerable monetary and time expense where a large number of part numbers are manufactured by use of such mold tools. Even when the mold system is balanced, later variations which may occur in the manufacture of insert and skin components may require that the mold tools be rebalanced to accomodate such later discovered variations.